Production of composite pigments containing titanium dioxide



Patented June 24, 1930 um'rao STATES PATENT OFFICE JOSEPH BLUMENFELD, OF PARIS, FRANCE, ASSIGNOR TO COMMERCIAL P IGMENTS CORPORATION, OF NEW YORK, N. Y., A CORPORATION OFDELA'WARE PRODUCTION OF COMPOSITE PIGMENTS CONTAINING TITANIUM DIOXIDE Ho Drawing.

My invention relates to a process for producing composite pigments containing titanium dioxide and pertains more especially to a means for coating secondary pigment particles with particles of TiO,, many of which are ultra-microscopic in size. In the present specification the term secondary pigment is used to denote any other pigment with which it is desired to blend titanium dioxide.

Titanium dioxide, which is alsodescribed in the older literature as titanium hydrate, hydrated titanic acid, and titanium hydroxide, is a white substance possessing superior pigment qualities. It is characterized by its very high opacity or hiding power and hence is a most suitable material for admixture with otherpigments to produce composite pigments.

In the prior art, many proposals have been made for the admixture of titanium dioxide with secondary pigments such as zinc oxide, barium sulfate, white lead, calcium sulfate, lithopone, and the like. Composite pigments have been prepared by the simple mixing of titanium dioxide with secondary pigments, this mixing having been accomplished in both dry and wet conditions. Various other schemes have been advanced in which titanium dioxide has been precipitated from solutions, by chemical means, in the presence of particles of sec- The present invention relates to an improvement in the production of composite pigments and comprises an easily controllable process, free from such complicating problems as are involved in the use of elevated temperatures or pressures, or highly corrosive solutions, by which particles of secondary pigment may be coated with particles'of titanium dioxide, many of which are of ultra-microscopic size. .The process consists in suspending particles of secondary pigment in an aqueous colloidal dispersion of titanium dioxide and coagulating titanium dioxide on said particles, by destroyingsaid dispersion. j

The composite pigment thus produced is Application filed March 13, 1928. Serial 170. 261,421.

then recovered by filtration and may be washed, dried, or calcin'ed as desired.

A suitable colloidal dispersion of titanium dioxide may be prepared from titanium dioxide precipitated from titanium solutions hydrolysis. Titanium dioxide precipitated by the hydrolysis of titanium-sulfuric acid solutions, as described in my U. S. Patent 1,504,672, is in the meta-titanic form,

since it is the result of a precipitation from a hot solution. For this reason, colloidal TiO prepared from this material is insoluble in acids, and thus difiers from colloidal ortho-titanic acid (ortho-titanium dioxide),

which has been described in the scientific literature. Titanium dioxide prepared by the hydrolysis of a sulfate solution wi]l'con-.

tain from 38% of adsorbed sulfuric acid, and it is necessary to remove this acid before the colloidal dispersion may be produced. This may be conveniently accomplished by as desired. The acid is incorporated with the filter cake by, any convenient method of admixture, whereupon the mass becomes enwashing the precipitate with an alkaline-sotirely fluid, owing to the conversion of the precipitated -TiO to the colloidal form, the

result being a suspension or dispersion of the particles in the water formerly adsorbed by the precipitated TiO filter cake. This phenomenon is known as eptization and the product is ordinarily escribed as a peptized solution.

In place of hydrochloric acid other substances which diminish the silriace tension.

of the liquid phase may be used in the same manner. For example, nitric acid or hydrobromic acid give the same client.-

In preparing a peptizedTrQg'solutlon for incorporation with 0 1 0 p1gments.

where the presence of a relatively small amount of an inert foreign substance is unobjectionable, I may combine the steps of removing adsorbed sulfuric acid from the TiO and peptizing the same. This may be done by mixing the moist preci itated TiO (e. g. the filter cake from which the mother liquor has been removed by washing) with a solution of barium chloride or calcium chloride. By this procedure, insoluble barium or calcium sulfate is produced and the free sulfuric acid which inhibits peptization is converted to an unreactive form. The hydrochloric acid generated by the reaction t en peptizes the TiO as formerly described.

- The particles of insoluble sulfate may be removed from the peptized solution by decantation, after settling, but since these substances are white inert materials of pigmentary value, it is not usually necessary to separate them from the peptized solution.

The aqueous colloidal dispersion (peptized solution) of TiO thus prepared is then mixed with the secondar pigment. This may be accomplished by a ding the dry pigment particles to the pe tized solution, with stirring, or by adding t e peptized solution to a separate aqueous suspension of the secondary pigment. The colloidal character of the TiO is in no way dependent upon the concentration of water present; consequent- 1y, one may use as much additional water as is necessary to make the mixing process hen the peptized titanium dioxide solution has been mixed with the secondary pigment, the TiO may be thrown out of its colloidally dispersed state and caused to coagulate itself on the pigment particles in.

peptizing acid and thus coagulate the colloidal articles. a

During the coagulation of the pe tized solution, the mixture should preferab y be a tated, to insure an even de sition of Ti%; partlcles on the particles 0 secondary pigment. After the coagulation of the peptlzed solution, the com osite pigment thus formed is recovered by ltration and is washed to remove soluble materials. The dry roduct may be calcined, ound, or otherwise treated, prior to actua use as a pigment.

It is then dried.-

Now, having described my invention, I shall give a specific example of its use:

A peptized\TiO solution containing approximately 1,200 grams of titanium dioxide colloidally dispersed in an aqueous mixture of about 2,500 grams of water and grams of hydrochloric acid is diluted with an equal volume of water. 5,000 grams of blanc fixe (barium sulfate) is gradually added to this mixture with stirring. When the incorporation is complete, about 50 grams of sulfuric acid (in either concentrated or diluted solution) is added, the stirring being con tinued. The addition of the sulfurlc acid causes the peptized titanium dioxide to be thrown out of the a ueous dispersion and to be coagulated on t e secondary pigment particles. Stirring is continued for about alf an hour, after which the slurry is put through a filter ress, washed with water to remove traces of acid, and dried. In place of sulfuric acid, a soluble sulfate may be employed as the coagulant.

The dry mass may be used as a pigment after being milled sufliciently to break up any large fragments formed during the drying operation though calcination at 900- 1000 for a ew minutes will improve its properties. In this manner a composite pagment containing about 20% of titanium oxide in the form of extremely small particles, some of which are of ultra-microscopic siz'e, is prepared. The titanium dioxide particles are preci itated in the pores of the blancfixe partic es, and a pigment of superior hiding wer results.

The s eci 0 example described is merely illustratlve and wide variations may be made without de arting from the spirit of the invention. or example, in place of blanc fixe, any other secondary pigment might be used in exactly the same manner. Among such secondary pi ments the following may- 'be mentioned:' si 'ca, white lead, ground barytes, zinc oxide, zinc sulfide, lithopone, calcium 0 rbonate, barium carbonate, cal cium sulf etc.

Some of these pi cuts are easily attacked 'by dilute acids, suc as are used for peptization, but this circumstance does not seriously interfere with the production of the compositepigments. The process of mixing the peptized solution with the secondary pigment is not an extended one and as soon as admixture is com leted, coagulation may be immediately need and the com ite igment maybe washed free from acid beore much reaction has occurred. In any case, however, the trouble may be obviated by using an alkaline substance such as ammonia or sodium carbonate as the coagulat ing agent, by which means the peptizing acid is neutralized and any dissolved pigment is re-%rhecipitated.

ile in the specific example given, 20%

of titanium dioxide was added to the secondary pigment, it is obvious that any other desired proportion might be incorporated by the same method.

Now, having described my invention, ll claim:

1. A process which comprises mixing pig- I ment particles with an aqueous colloidal dispersion of titanium dioxide, adding a coagtaining colloidal titanium dioxide and a eptizing quantity of hydrochloric acid, ad ing sulfuric acid to coagulate the colloidal titanium dioxide and recovering the composite pigment thus formed,

5. A process which comprises mixing one of the pigments of the group consisting of silica, barium sulphate, calcium sulphate and lithopone with an aqueous colloidal dispersion of titanium dioxide, adding a coagulant and recovering the composite pigment thus formed.

6. A process which comprises mixing pigment particles in an aqueous mixture containing colloidal titanium dioxide, adding a polybasic acid to coagulate the colloidal titanium dioxide and recovering the composite pigment thus formed.

7. A process which comprises mixing pigment w1th an aqueous colloidal dispersion of titanium dioxide, adding a coa lant, recovering the composite precipitate thus formed, and calcining it at 9001000 C.

8. A process whlch comprises mixing titanium dioxide filter cake with a solution of alkaline earth chloride to produce a peptized titanium dioxide solutlon, mixing a pigment with the peptized titanium dioxide solution, adding a coagulant and recovering the composite pigment thus formed.

- JOSEPH BLUMENFELD. 

